Click on the hat and wrench icon, and choose to 'Like' Bad Piggies on Facebook, and you'll receive three free hint tokens.
Longer vehicles are less likely to tip over than small ones.
Certain objects (bottle rockets etc) if you can tap them in the vehicle editor you'll be able to rotate them.
Keep in mind that you can change how a vehicle acts and moves by moving the objects in and around your fly machine thus shifting weight means manipulating fly abilities.
Use TNT if you want to send a piggy a long way but be cautious.
Umbrellas can be used to slow down and float safely towards the ground.
Stars are placed in some pretty devious places, including the opposite way of the goal. Always survey the level completely before you begin constructing a vehicle.
You don't need to hit all three goals in one go. Instead, you can make vehicles tuned for speed or durability and achieve the goals on separate runs.
Use the pinch gesture to zoom in and out of the level, and see the entire scenario in one go.